Electrophotographic imaging and copying process



United States Patent 3,363,556 ELECTRGFHOTOGRAPHIC IMAGING AND COPYINGPROCESS Benjamin L. Shely, White Bear Lake, and Joseph W.

Shepard, St. Paul, Minn., assignors to Minnesota Mining andManufacturing Company, St. Paul, Minn, a corporation of Delaware NoDrawing. Filed Mar. 22, 1962, Ser. No. 181,706 (Claims. (ill. 101-469)This invention relates to an integrated process for the reproduction ofa light image and to materials employed therein. In one aspect, thisinvention is directed to a process for the production of multiple printsfrom a light image. In still another aspect, this invention relates to aprocess for preparing a master copysheet of a light image which can beused to provide multiple copies thereof.

A recently developed image reproduction process involveselectrolytically developing permanent and visible images on suitable,strongly photoconductive copysheets after exposure to light images. Thisprocess, described more fully in United States Patent No. 3,010,883,includes the electrolysis of an electrolytic developer and particularlythe selective electrodeposition of a metallic or other visibly distinctcoating at the exposed portions of the photosensitive surface, e.g. byelectrolytic reduction. Strongly photoconductive copysheets suitable foruse in the above method are described in United States Patent No.3,010,884. To improve the sensitivity of such photoconductivecopysheets, various optical sensitizers have been suggested. However,many of the dye sensitizers tend to discolor the surface of thephotoconductive copysheet and detract from the quality of the imageproduced thereon. In addition, it has been desired to provide a simple,eflicient means for making multiple copies from the electrolyticallydeveloped copysheet.

It is therefore an object of this invention to provide a simple,economical method for making multiple copies of a radient image.

It is another object of this invention to provide a method for utilizingan electrolytically developed,

strongly photoconductive copysheet as a master for the thermalpreparation of a heat stable copy thereof.

Still another object of this invention is to provide a reproductionprocess involving a photoconductive copysheet in which the visibleappearance of the photoconductive copysheet, both prior and subsequentto electrolytic development, does not substantially affect the copiesproduced therefrom.

Yet another object of this invention is to provide a process forpreparing multiple copies of a light image.

Still another object is to provide a process for the preparation ofmultiple copies of a radient image from a reusable photoconductivecopysheet.

As used herein, thermal processes refers generally to processesrequiring the use of heat.

The process of this invention comprises exposing photoconductive,electrolytically developable copysheet to produce a differentialconductivity pattern thereon, electrolytically forming a pattern of avaporizable image forming material on the exposed surface correspondingto said differential conductivity pattern, positioning said surface ofthe copysheet adjacent a receptor surface, and heating said copysheet toaffect the selective vapor transfer of said vaporizable image formingmaterial to said receptor surface and the formation on said receptorsurface of a visible image corresponding to said differentialconductivity pattern. In one embodiment the image forming material istransferred as a vapor to a receptor (usually in sheet form) containinga color-forming coreactant, the

vaporized image forming material and the color-forming ice coreactantinterreacting on said receptor to form visibly distinct image areas. Inanother embodiment, where the vaporized image forming material is itselfstrongly colored, no further reactant is required on the receptor, andthe receptor sheet color provides a visible contrast with the imageforming material condensed thereon.

Strongly photoconductive copysheets suitable for the practice of thisinvention include those described in United States Patent No. 3,010,884and generally comprise a strongly photoconductive layer containing suchmaterials as photoconductive zinc oxide, photoconductive indium oxide,etc., superimposed on a contiguous, electrically conductive backing orsupport, such as aluminum foil. Optical sensitizers, e.g. Acridineorange, may be incorporated into the photoconductive layer to improvethe spectral response. Since the color of the copysheet does notnecessarily affect the quality of the thermally prepared copies, theamount of sensitizer in the photoconductive layer can be varied widelyto achieve optimum results. The photoconductive layer may be overcoatedwith a Water permeable layer, such as a fihn form ing silica. Fihnforming silicas are generally capable of forming a stable aqueouscolloidal sol with a particle size in the 1 to 100 millimicron diameterrange, preferably from about 10 to about 50 millirnicrons, and theirprep ration may be effected by procedures described in United StatesPatent No. 2,244,325. Further description of such electrolyticallydevelopable photoconductive copysheets having glossy, water permeable,cohesive and relatively transparent silica films superimposed on thephotoconductive layer is given in United States Ser. No. 140,032, filedSept. 2, 1961, now US. Patent 3,127,548.

After exposure of the photoconductive copysheets to a source ofactivating irradiation, e.g. actinic irradiation such as visible light,X-rays, electron or proton beam, etc., a differential electricalconductivity pattern is created in the photoconductive layer,corresponding to the information carried by the activating irradiation,and is utilized for selectively creating on the conductive areas byelectrolytic means a pattern of vaporizable image forming material.Exposure of and electrolytic deposition on such strongly photoconductivecopysheets is described in United States Patent No. 3,010,883, asmentioned earlier.

For purposes of this invention, vaporizable image forming material isdefined as a material readily vaporized at temperatures above roomtemperature and below 300 (1., preferably between about C. and about 250C., and which is capable of affecting a color change either by chemicalreaction with other chemical compounds or, when itself strongly colored,by condensation from the vapor onto a surface Without chemical reaction.Whether the vaporizable image forming material is of the reactive ornon-reactive type, therefore, it should be essentially non-vaporizing atnormal room and storage conditions and can be described as normallysolid under such conditions.

A variety of techniques may be used to convert the differentialconductivity pattern of the exposed copysheet into a differentialpattern of the vaporizable image forming material. However, in everyinstance, the conversion is accomplished electrolytically orelectrophoretically. For purposes of this invention, both electrolyticand electrophoretic will be generically described as electrolytic,although electrophoresis involves the use of charged particles otherthan charged ions. In practice,

the vaporiz-able image forming material may be selectively deposited onthe copysheet surface by electrolysis (with or without furthermodification thereon) or a thin film of vaporizable image formingmaterial may be uniformly provided on the copysheet surface andelectrolytically modified in selected areas to alter its vaporizabilityand/ or its image forming properties. The former will be referred to aselectrolytic deposition, and the latter will be referred to aselectrolytic modification, it being understood, however, that bothtechniques may be employed simultaneously.

Electrolytic deposition is accomplished by depositing the normallystable vaporizable image former directly from solution or suspension.When the electrolytic bath contains the vaporizable image former or itselectrolytic precursor in solution, the copysheet is connected either asanode or cathode, depending on the electrical charge of the ions. Whenthe electrolytic bath contains the vaporizable image former or itselectrolytic precursor in suspension, a suitable charge bearing carrier,e.g. colloidal alumina, is preferably used to effect migration towardthe copysheet surface, where it is deposited. In such a depositionprocess, the vaporizable image forming deposit may consist of aninterreactive volatilizable image forming compound which, upon vaportransfer from the copysheet to the receptor, reacts with a coreactantthereon to form a visible image. Such interreactive volatilizable imageforming compounds include, for example, oxidizing and reducing agents,the corresponding coreactant being a compound which alters its colorvalue upon oxidation or reduction respectively. One preferred class ofinterreactive volatilizable image forming compounds are prepared fromthe quaternary ring bases. Illustrative of the useful quaternary ringbases are l-ethyl quinolinium iodide, l-ethyl quinoldinium iodide,l-ethyl pyridinium bromide, l-ethyl- 2,6-dimethyl quinolinium iodide,l-butyl pyridinium, bromide 1-ethyl-2-methyl pyridinium bromide,1-ethyl4- methyl pyridinium bromide, etc., which electrolyticallydeposited the corresponding organic reducing agent at the cathode fromaqueous medium. Other suitable materials which electrolytically deposita volatilizable reducing agent include quinone, aromatic nitro compoundscapable of reduction to amines, aromatic hydroxyl amines, etc.Volatilizable oxidizing agents, e.g. the oxidation product ofhydroquinone, catechol, tetrachlorohydroquinone, tetrahromohydroquinone,aminophenol or oxidizing agents such as N-chlorosulfonamides, etc. canalso be electrolytically deposited when the copysheet is connected asanode, usually from an electrolyte containing appropriate chargedparticles.

Reducible coreactants, such as silver behenate, etc. contained uniformlyon the receptor sheet may be reduced by a vaporized reducing agent,producing a color change on the receptor. The reducible coreactants onthe receptor sheet, on the other hand, may be themselves intenselycolored and capable of losing or changing color intensity or value uponcontact with a vaporized organic reducing agent, as illustrated byreducible dyes, such as methylene blue, crystal violet, and Malachitegreen. If the receptor sheet contains a relatively colorless compoundwhich forms a colored complex, the vaporizable image forming depositsmay contain the corresponding complexing agent, e.g. catechol (forms acomplex with iron compounds), thereby forming the colored complex of thereceptor sheet upon vapor transfer.

As mentioned earlier, when the vaporizable image forming material isitself intensely colored, it may be transferred directly in vapor formto the receptor surface, where its condensation forms a visible patterncorresponding to the original image without further chemical reaction.No coreactant is thus required on the receptor sheet. Both water solubleand water insoluble dyestuffs may be deposited, the latter beingdeposited from a colloidal suspension, preferably from a suspension ofpositively charged particles.

Electrolytic modification may also be used to provide a selectiveimagewise coating of vaporizable image forming material on the copysheetsurface. Instead of electrolytically depositing the vaporizable imageformer, the copysheet may be coated uniformly with a thin film of amaterial which is then modified by the electrolytic reaction to alterits vaporizability and/ or its image forming properties. Thismodification may be accomplished by selective electrolytic destruction,electrolytic masking or electrolytic immobilization of the vaporizableimage forming material on the more conductive areas of the copysheetsurface, as is hereinafter described.

The mechanism of electrolytic destruction of a vaporizable image formercan be accomplished by electrolytic oxidation of a vaporizable reducingagent uniformly coated on or included in the copysheet surface. Suchreducing agents including pyrogallol, catechol, methyl gallate,aminonaphthols, 4mcthoxy naphthol, etc., which are anodically oxidizedon the more conductive areas of the copysheet surface. Reduciblecoreactants, e.g. silver behenate, etc. contained on the receptor sheetare then reduced when contacted with the vaporized, unoxidized reducingagent, thereby producing a visible color change on the receptor surfaceand a visible reproduction of the original image. These vaporizablereducing agents may also be electrolyzed cathodically in a medium thatprovides a relatively high pH in the light struck areas, e.g. an aqueousbath containing soluble magnesium salts. When exposed to air in such ahigh pH environn ent, the vaporizable reducing agents (eg. 4-rnethoxynaphthol) are readily oxidized in the more conductive areas, thusleaving the unoxidized reducing agent only in the background areas forvapor transfer to the receptor sheet and interreaction with silverbehenate or other suitable material which changes color value uponreduction.

The mechanism of electrolytic masking involves a photoconductivecopysheet containing on or immediately under its surface a uniform layerof a vaporizable image former and the selective electrolytic depositionsof a mask or coating to cover or fix such image forming compound in themore conductive areas. The mask is usually a higher molecular weight,e.g. polymeric, material which is desirably deposited from latex andwhich provides a relatively impermeable barrier to vapor. Eithercathodic or anodic deposition may be used, depending on the charge onthe latex particles. Illustrative of suitable masking materials of aninsulative nature are the organic chelates or coordination compounds andamine derivatives, such as amine salts or quaternaries, including theWerner type chromium of fatty acids (e.g. Quilon chrome complex, aproduct of E. I. du Pont de Nemours and Co., Wilmington, Delaware),various fatty amine derivatives (e.g. Armeens and Arquads, ArmourIndustrial Chemical Co., Chicago, Illinois), amine containing resins(e.g. Versamid resins, General Mills, -Inc., Minneapolis, Minnesota),condensation products of polymerized unsaturated fatty acids (e.g.'dilinoleic acid) with aliphatic amines (e.g. ethlylene diarnine),polyethylene, polytetrafluoroethylene, polytrifluorochloroethylene,synthetic rubbers, polyvinyl acetate, polystyrene, butadiene-styrenecopolymers, butadiene-acrylic acid copolymers, natural rubber,polyviny-lidene chloride, etc. After the deposit of sufficient maskingmaterial to inhibit the vapor transfer of the image forming material inthe image areas, the unmasked image former in the background areas ismore readily transferred in vapor form to the receptor sheet.

Electrolytic immobilization also provides a method for creating an'imagewise coating of vaporizable image forming reactant on thecopysheet surface. In contrast to techniques which alter the imageforming properties of the vaporizable material, this method generallyinvolves a change in vaporizability of the image former. The copysheetsurface may be coated with a vaporizable image former which forms acomplex or chelate of lower vaporizability, e.g. chelating or complexingof a phenolic reducing agent, coated uniformly over the copysheetsurface, by cathodic electrolysis of a metal ion that complexes with thephenolic reducing agent. As one specific example, if a copysheet isuniformly coated with catechol and exposed to a light image, cathodicelectrolysis with an electrolytic bath containing ferrous or ferric ionproduces a colored complex in the more conductive (and more alkaline)areas of the copysheet surface. This complex has significantly lowervaporizability than the cate chol. Hence, upon the uniform applicationof heat to the copysheet, only the free catechol in the background areasis vapor transferred to the receptor sheet, where the catechol reduces amaterial, such as silver behenate, or forms a complex with anothermaterial thereon to produce a visible image.

In the electrolytic modification techniques, the vaporizable imageforming material may be coated uniformly in a thin tfilm over thephotoconductive surface of the copysheet after exposure to the lightimage and before electrolysis. When the film of vaporizable imageforimng material is relatively transparent to the activating irradiationincident to exposure and creation of a differential conductivity imagepattern on the copysheet, it may of course be present over thephotoconductive surface before exposure. It has been found thatextremely small amounts of the vaporizable image forming materialuniformly distributed over the copysheet surface are effective for thethermal preparation of multiple copies from the copysheet in thismanner. As mentioned earlier, the vaporizable image forming material mayalso be included in a coating in or near the surface of thephotoconductive copysheet.

As receptor surfaces, it is possible to use fabric, paper, plastic film,metal foil or plate, etc. 'Porous flexible sheets are sometimesdesirable if an image forming coreactant is incorporated either in thereceptor sheet or on the surface thereof. Transparent receptor sheetsmay be used to provide transparencies from which projected light imagescan be obtained. This is often important if an enlargement of the imageis desired, as in the case of microfilm.

Both positive and negative prints can be obtained on the receptorsheets. For example, if the receptor sheet contains a colored coreactantwhich is rendered colorless by reaction with a reducing agent vaporizedfrom the more conductive areas of the copysheet, a positive of theoriginal radient image may be obtained. Conversely, if the coreactant isreduced to a more intensely colored product, a negative print may beobtained. Methylene -blue, Crystal Violet and Malachite green, whencontained in the receptor sheet, are examples of coreactants which areconverted to a colorless form upon reduction. Silver behenate andtetrazolium compounds exemplify coreactants which become more intenselycolored upon contact with a vaporized reducing agent.

After the photoconductive copysheet has been exposed to the irradiantimage, or simultaneous therewith, it is electrolytically developed toprovide a difierential deposit of vaporizable image forming material onthe photoconductive surface using any of the electrolytic deposition orelectrolytic modification techniques described earlier.

When such photoconductive copysheets are connected asanodes duringelectrolytic development, a rectification effect has been observed whichtends to increase the overall resistance to current flow. By providing arelatively light transmissive, electrically conductive surface coatingon the photoconductive layer (e.g. metal, etc.) as described in US.Patent application Ser. No. 113,290, filed May 29, 1961, now US PatentNo. 3,127,333, this rectification barrier may be markedly reduced, andanodic electrolytic development of the photoconductive copysheet isfacilitated.

After electrolytic development, the copysheet is then placed in closeproximity to, preferably in physical contact with, a receptor sheet.Heating the copysheet slightly above the vaporization point of thevaporizable image former, typically by passing both the copysheet andthe superimposed receptor sheet through a heated mangle, ironing deviceor commercial thermographic copying machine with the heat beingpreferably applied to the backside of the photoconduct-ive copysheet,vaporizes the image forming material and affects its vapor transfer into7 the adjacent receptor sheet. This vapor transfer step can be repeatedwith one or more receptor sheets to make multiple copies from thephotoconductive copysheet master until the vapor supply is exhausted.The application of heat to the copysheet also tends to erase thedifferential conductivity pattern thereon, thus in some cases permittingreuse of the copysheet upon exhaustion of the vaporizable image formeron its surface.

Apparatus suitable for heating the copysheet may conveniently consist ofa line source of light including a tubular bulb having a linear filamentand mounted within a focused reflective housing, as described in UnitedStates Patent Number 2,740,895. Another suitable form of apparatus isdescribed in United States Patent Number 2,891,- 165. A heated platenmay also be employed.

The following examples will illustrate the invention and are notintended to limit the scope thereof.

Example I This example illustrates the cathodic electrolytic depositionof an organic reducing agent.

A photoconductive copysheet containing a strongly photoconductive layerof zinc oxide and butadiene-styrene copolymer (30:70 mol ratio) in apigment to binder ratio of about 4/ 1 as binder on an aluminum foilbackin-g was exposed to a visible light image. The exposed copysheet waselectrolytically developed, the aluminum backing being connected ascathode, by slowly passing a sponge developer roller (anode) over thesurface with the application of a 40 Volt DC. electrical potential. Thesponge developer roller contained a 5% aqueous solution of lethylpyridinium bromide. The thus developed copysheet was then placed againsta paper receptor sheet containing silver behenate and heated betweenmetal plates for ap-v proximately one second at 120 C. Hot rollers orany other means for uniformly heating the copysheet for a specific timeinterval may also be used. A brown-black negative image is developed onthe receptor sheet. This operation can be repeated to obtain furthercopies in the same manner and permits the preparation of multipleenlarged prints from a microfilm transparency. The final prints onapaque receptor sheet material are directly readable if the originalvisible light image is a mirror image of the desired print.

Example II This example illustrates the preparation of a transparencyusing the cathodic electrolytic deposition of an organic reducing agent.

A transparent receptor sheet was made by coating a polyethyleneterephthalate film with an alcoholic solution of triphenyl tetrazoliumand butyral polyvinyl plastic. Following the procedure set forth inExample I, a negative transparency was produced on the receptor sheetafter heat treatment at C.

Example III This example illustrates the preparation of a positivetransparency or opaque print using electrolytic deposition of an organicreducing agent.

A receptor sheet previously primed with colloidal silica was treatedwith a 3% solution of crystal violet in ethyl alcohol to form a bluecolored receptor sheet. A photoconductive zinc oxide copysheet was thenexposed to a visible light image and electrolytically developed with a5% solution of l-ethyl pyridinium iodide in the manner described inExample I. The exposed copysheet was then placed against the bluecolored receptor sheet and heated briefly to C. A positive white on bluecopy was obtained, the crystal violet being reduced to leuco form in theareas corresponding to the visible light struck areas of thephotoconductive copysheet.

Example I V This example illustrates the electrolytic deposition of avaporizable dyestuff.

Two-hundred grams of water and 6 grams of colloidal alumina (AlOOH) weremixed in a blender for minutes. Three grams of DuPont Oil Yellow N, awater insoluble dye (Color Index 11020) was then added and dispersed byfurther blending for minutes. A photoconductive zinc oxide copysheet ofthe type described in Example I was exposed to a visible light image andwas electrolytically developed using the above dispersion, the copysheetbeing connected as cathode. After less than 5 seconds at a potential of40 volts DC. the colloidal alumina (the particles of which bear apositive charge) and dye deposited selectively on the light struck areasof the copysheet surface. The copysheet was then removed from theelectrolytic bath, the dyed surface placed in contact with a paperreceptor sheet, and heat was applied uniformly over the back of thecopysheet (about 250 C.). After separating the sheets a yellow imagecorresponding to the original light image was formed on the receptorsheet.

Example V This example illustrates the electrolytic deposition of avaporizable chelating agent.

Two-hundred grams of water and 6 grams of colloidalalumina (AlOOH) wereblended for five minutes. Then three grams fo dimethylglyoxime, a waterinsoluble complexing agent, was added and dispersed by further blendingfor 10 minutes. A photoconductive copysheet, as described in Example I,was exposed to a visible light image and was electrolytically developedusing the above dispersion, the copysheet being connected as cathode.After less than 5 seconds at a potential of 40 volts DC. the colloidalalumina and dimethylglyoxime had deposited on the light struck areas ofthe photoconductive surface. This copysheet was then removed from theelectrolytic bath, and the photoconductive surface thereof was placed incontact with a receptor sheet containing a nickel soap. The back of thecopysheet was heated briefly and uniformly to 250 C. Upon separating thesheets, the receptor sheet was observed to contain a red image formedfrom the nickel-dimethylglyoxime complex. Ten copies were prepared fromthis copysheet by repeating the heating sequence with further similarreceptor sheets.

Example VI This example illustrates the electrolytic destructiontechnique in which an organic vaporiza'ble reducing agent is selectivelyoxidized in a high pH environment.

A photoconductive copysheet having a coating of zinc oxide andbutadiene-styrene copolymeric binder (4/ 1 wt. ratio) on an aluminumfoil backing was coated with a thin film of 4-methoxy naphthol andbuffed lightly to insure a thin continuous coating. The copysheet wasdark adapted and exposed to a light image. With the aluminum foilconnected as cathode, a porous plastic (Porelon) roller containing a 5%aqueous solution of cesium nitrate was passed slowly over the surface.The anode was embedded in the roller. The potential applied was 40 voltsD.C. After electrolytic development the increased alkalinity of the moreconductive areas caused the 4-methoxy naphthol thereon to oxidize whenexposed to air. The copysheet was then placed adjacent to a paperreceptor sheet containing silver behenate and heated at 120 C. to form avisible blue-black positive image on the receptor sheet. The heatingstep was repeated to provide multiple copies.

Other suitable electrolytes are ioniza'ble salts of barium, magnesium,calcium, potassium and sodium. Hydroquinone operated in similar. fashionwhen used in place of 4- methoxy naphthol.

Example VII This example will illustrate electrolytic immobilization bymeans of chelate formation.

A dark adapted photoconductive copysheet, as in Example I, was coatedwith catechol and exposed to a light image and was cathodicallyelectrolyzed in similar fashion.

The porous roller contained a 5% aqueous solution of ferrous ammoniumsulfate. The electrolyzin-g voltage was 20 volts D.C. The ferrous ionreacted with the catechol in the light struck areas, forming a coloredcomplex having a lower vaporizability than catechol. When theelectrolytically developed copysheet was placed adjacent a receptorsheet containing silver behenate and heated to C., a positive visibleimage was produced on the receptor, the silver behenate being reduced byvaporized catechol.

In a similar fashion, a dithiooxamide can be electrolytically complexedwith nickel, using an aqueous nickel salt electrolyte, and theuncomplexed dithiooxamide can be vapor transferred to a receptor sheetcontaining a complexible nickel salt, producing a positive print.

Example VIII This example illustrates electrolytic destruction by anodicelectrolytic oxidation of a vaporizable reducing agent.

A photoconductive zinc oxide copysheet similar to that described inExample I was uniformly vapor coated on the zinc oxide surface withaluminum, the aluminum layer having a 30% transmissivity to visiblelight from a tungsten source. The vapor coated surface was then coatedby buffing with 4-methoxy-l-naphthol, and the resulting sheet wasexposed to a light image. With the electrically conductive substrate ofthe copysheet connected as anode, electrolytic development wasefit'ected for 3 seconds at 40 volts D.C., using a 5% aqueous solutionof sodium acetate as the electrolytic bath. This resulted in theselective oxidation of the 4-methoxy-l-naphthol in the light struck, andhence more conductive, areas of the copysheet surface. When this sheetwas then placed in contact with a paper receptor sheet containing silverbehenate and heated at 120 C., a positive image was formed on thereceptor.

Similar results were achieved with photoconductive copysheets having acoating of carbon black in a butadiene-styrene copolymer rnatrix (10-20%transmissivity to visible light) instead of vapor coated aluminum. Vaporcoated semiconductors, such as p-type lush, and other materials havingrelatively low lateral and relatively high transverse electricalconductivity may also be used as topcoatings for the photoconductivelayer, provided such layers permit transmission of sufiicient radientenergy to activate the underlying photoconductive layer.

Example 1X This example illustrates electrolytic masking.

A photoconductive Zinc oxide copysheets, as described in Example I, wassurface coated with DuPont Oil Yellow N (Color Index 11020). Thecopysheet was then exposed to a visible light image, forming acorresponding conductive pattern thereon. With the electricallyconductive substrate of the copysheet connected as cathode, electrolyticdevelopment was effected for 3 seconds at 45 volts DJC. using a 3% waterdispersion of colloidal alumina (AlOOI-I) as the electrolytic bath. Thepositively charged alumina particles deposited selectively on the moreconductive areas of the copysheet surface, forming a barrier coatingover the yellow dye. This developed sheet was then placed in contactwith an ordinary sheet of paper and heated at 250 C. to form a positivedye image on the paper surface.

Example X This example illustrates electrolytic destruction by selectiveanodic oxidation of a reducing agent.

An aluminum vapor coated photoconductive copysheet, as described inExample VIII, was buffed lightly on the aluminum surface with a 2%solution of hydroquinone in methyl alcohol. After exposure to a lightpattern to form a conductive pattern on the copysheet, using theelectrically conductive substrate of the copysheet as anode,electrolytic development was effected for three seconds at 40 voltsD.C., using a 5% aqueous solution of sodium acetate as the electrolyticbath. This resulted in the selective oxidation of the hydroquinone toquinone on the light struck areas. When this sheet was placed in contactwith a paper receptor sheet containing silver behenate and heated atabout 120 C., the vaporized hydroquinone transfers to the receptor andreduces the silver salt to free silver, forming a positive print. Whenthe paper receptor sheet contained red colored 1,3,5-triphenyl formazan,the vaporized quinone oxidized and decolorized the red formazan forminga negative print. If the leuco form of Malachite green (Color Index4200) is contained in the receptor, the vaporized quinone oxidizes theleuco form to its green colored form, producing a positive print.

Similarly, the copysheet can be coated with quinone and cathodicallyelectrolyzed to form hydroquinone on the light struck areas.

Example XI This example illustrates electrolytic modification bycathodic electrodeposition of an oxidizing agent and the oxidationthereby of a vaporizable reducing agent.

A photoconductive zinc oxide copysheet, as described in Example I, wasexposed to a visible light image and electrolytically developed with anaqueous solution con taining 3 Weight percent K Cr O and 3 weightpercent NiCl The nickel chloride can be replaced with CoCl or MnCl whichalso form relatively water insoluble metal chromates. The electricallyconductive backing of the copysheet was connected as cathode duringelectrolysis (40 volts DC. for about 3 seconds). During cathodicelectrolysis the more conductive areas of the copysheet surface becamemore alkaline, and insoluble nickel chromate precipitates selectively Onthose surface areas. After the electrolytic step is completed, thecopysheet surface is buffed lightly with 4methoxy naphthol. On thoseareas having the nickel chromate deposits the 4-methoxy naphthol isoxidized. When the copysheet was placed adjacent a receptor sheetcontaining silver behenate and heated to about 120 C. for severalseconds, the unoxidized 4-methoxy naphthol in the background areas vaportransferred to the receptor and reduced the silver behenate to freesilver, forming a positive print.

Other vaporizable reducing agents, such as hydroquinone, can be used inplace of the 4-methoxy naphthol to produce similar results. Withhydroquinone the oxidation product, i.e. quinone, can also be utilizedin conjunction with a receptor sheet containing an oxidizable material,e.g. leuco Malachite green (Color Index 4200).

Example XII Grams Deionized acid silica sol (34% solids in water;particle size, 1622 millimicrons, Nalcoag 1034A) 50 Water 3O Isopropylalcohol 20 Dithiooxamide 2 After the top coated copysheet was allowed todry under ordinary room conditions for several hours, it was exposed toa light pattern and was then cathodically electrolyzed for 1 to 3seconds (40 volts DC.) in a aqueous solution of ethyl pyridiniumbromide. When the electrolyzed copysheet had dried, it was placedadjacent a paper receptor sheet containing nickel stearate and washeated at about C. for several seconds. A blue positive image was formedon the receptor sheet, the vaporized dithiooxamide from the copysheetbackground areas reacting with the nickel stearate to form a blue nickelcomplex. No dithiooxamide transferred from the light struck areas of thecopysheet.

Various other embodiments of the present invention will be apparent tothose skilled in the art without departing from the scope thereof.

We claim:

1. An image reproduction process which comprises exposing to activatingirradiation a photoconductive, electrolytically developable copysheet toproduce a differential conductivity pattern thereon, electrolyticallydepositing from an electrolytic bath a vaporizable image formingmaterial selectively on the more conductive areas of said copysheet,positioning the electrolytically developed copysheet adjacent a surfaceof a receptor sheet capable of changing color upon contact with saidvaporizable image forming material, and heating said copysheetsufiiciently to effect vapor transfer of said vaporizable image formingmaterial to said receptor surface, thereby creating a visible image onsaid receptor surface corresponding to said differential conductivitypattern.

2. The image reproduction process of claim 1 wherein said vaporizableimage forming material is colored and the creation of said visible imageon said receptor surface results from condensation of said vaporizleimage forming material thereon.

3. The image reproduction process of claim 1 wherein said receptorsurface contains a material which chemically reacts with saidvaporizable image forming material and changes in color upon saidreaction.

4. The process of claim 1 in which said vaporizable image formingmaterial is an organic dye.

5. The process of claim 1 in which said receptor surface contains acoreaotant which reacts with said vaporizable image forming material toform a product which is more intensely color than said coreactant.

6. The process of claim 1 in which said receptor surface contains silverbehenate and said vaporizable image forming material is a reducing agentfor silver behenate.

7. The process of claim 1 in which said receptor surface contains acolored coreactant which reacts with said vaporizable image formingmaterial to form a product which is less intensely colored than saidcoreactant.

8. The process of claim 1 in which said receptor surface containsCrystal Violet and said vaporizable image forming material is a reducingagent for Crystal Violet.

9. The process of claim 1 in which said receptor surface is the surfaceof a transparent plastic sheet.

10. The process of claim 1 in which said receptor surface is the surfaceof a paper sheet.

References Cited UNITED STATES PATENTS 2,770,534 11/ 1956 Marx 101149.43,094,417 6/1963 Workman 101-149.4 3,106,518 10/1963 Reithel 101149.23,242,858 3/1966 Eastman et a1. 101 3,262,386 7/ 1966 Cordon 101149.43,280,735 10/ 1966 Clark et a1 101-149.4

DAVID KLEIN, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,363,556 January 16, 1968 Benjamin L. Shely et a1.

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 2, line 32, for "3,127,548" read 3,165,458 column 3, line 28, for"quinoldinium" read quinaldinium line 57, for "of" read on column 4,line 43, for "chromium of" read chromium complexes of column 6, line 41,for "apaque" read opaque column 10, line 31, for "vaporizle" readvaporizable line 42, for "color" read colored Signed and sealed this 1stday of April 1969.

5EAL) .ttest:

EDWARD J. BRENNER Commissioner of Patents dward M. Fletcher, Jr.

nesting Officer

1. AN IMAGE REPRODUCTION PROCESS WHICH COMPRISES EXPOSING TO ACTIVATING IRRADIATION A PHOTOCONDUCTIVE, ELECTROLYTICALLY DEVELOPABLE COPYSHEET TO PRODUCE A DIFFERENTIAL CONDUCTIVITY PATTERN THEREON, ELECTROLYTICALLY DEPOSITING FROM AN ELECTROLYTIC BATH A VAPORIZABLE IMAGE FORMING MATERIAL SELECTIVELY ON THE MORE CONDUCTIVE AREAS OF SAID COPYSHEET, POSITIONING THE ELECTROLYTICALLY DEVELOPED COPYSHEET ADJACENT A SURFACE OF A RECEPTOR SHEET CAPABLE OF CHANGING COLOR UPON CONTACT WITH SAID VAPORIZABLE IMAGE FORMING MATERIAL, AND HEATING SAID COPYSHEET SUFFICIENTLY TO EFFECT VAPOR TRANSFER OF SAID VAPORIZABLE IMAGE FORMING MATERIAL TO SAID RECEPTOR SURFACE, THEREBY CREATING A VISIBLE IMAGE ON SAID RECEPTOR SURFACE CORRESPONDING TO SAID DIFFERENTIAL CONDUCTIVITY PATTERN.
 3. THE IMAGE REPRODUCTION PROCESS FO CLAIM 1 WHEREIN SAID RECEPTOR SURFACE CONTAINS A MATERIAL WHICH CHEMICALLY REACTS WITH SAID VAPORIZABLE IMAGE FORMING MATERIAL AND CHANGES IN COLOR UPON SAID REACTION. 